High solids coating composition with oligomeric hydroxy phosphate catalyst-B

ABSTRACT

A fast curing, high solids coating composition which upon curing forms a hard, glossy, durable coating exhibiting excellent resistance to solvents and water. The coating composition which is particularly adapted for use as an automotive topcoat, contains greater than about 60 percent by weight of nonvolatile solids and, exclusive of pigments, solvents and other nonreactive components, consists essentially of: 
     (A) a bifunctional copolymer bearing hydroxy functionality and pendent epoxy functionality, having a number average molecular weight (M n ) of between about 1500 and about 10,000 and a glass transition temperature (Tg) of between about -25° C. and about 70°; 
     (B) a reactive catalyst comprising at least one oligomeric hydroxy functional organophosphate ester selected from certain mono- and diesters of phosphoric acid; 
     (C) an amine-aldehyde crosslinking agent; and 
     (D) optionally, a hydroxy functional additive. The oligomeric hydroxy functional organophosphate ester is included in the composition in an amount sufficient to provide between about 0.8 and about 1.5 equivalents of acid functionality for each equivalent of pendent epoxy functionality in copolymer (A), and the amine aldehyde crosslinking agent is included in the composition in an amount sufficient to provide at least about 0.4 equivalents of nitrogen crosslinking functionality for each equivalent of hydroxy functionality included in the composition.

BACKGROUND OF THE INVENTION

This invention is related to a fast curing, high solids, thermosettingcoating composition. More particularly, the invention relates to apolymeric, high solids, fast curing coating composition which isparticularly adapted to provide an automotive topcoat and whichdemonstrates hardness, high gloss, outstanding durability and excellentresistance to solvents and water. Still more particularly, thisinvention relates to a fast curing, high solids, thermosetting coatingcomposition adapted to be used as an automotive topcoat wherein thetopcoat includes metallic flake as a pigment.

Because of increasingly strict solvent emissions regulations in recentyears, low solvent emission paints have become very desirable. A numberof high solids paint compositions have been proposed to meet these lowsolvent emission requirements. However, many of these compositions aredeficient because of difficulty in application, slow curing rates, lackof flexibility, poor durability and low solvent and water resistance.Many of the proposed compositions have been particularly deficient asautomotive topcoats, particularly when the topcoat is to includemetallic flake as a pigment.

The deficiency in compositions including metallic flake results fromundesired reorientation of the metallic flake during application andcure of the coating. Flake reorientation results primarily because ofthe very low viscosity resins used in the paint compositions toaccommodate high solids. The low viscosity is not sufficient toimmobilize the flakes which tend to redistribute themselves to show"reverse flop" and nonuniform distribution.

The coating compositions of this invention combine the above discusseddesired properties and low application viscosity with rapid cure so asto overcome deficiencies of previously proposed high solids materialsand thereby achieve a high solids coating composition particularlyadapted for automotive topcoats including metallic flake as a pigment.

SUMMARY OF THE INVENTION

The thermosetting coating composition of this invention contains greaterthan about 60 percent by weight of nonvolatile solids, preferablygreater than about 70 percent by weight, and is capable of curingrapidly at a low temperature. The composition, exclusive of pigments,solvents and other nonreactive components, consists essentially of:

(A) a bifunctional copolymer bearing hydroxy functionality and pendentepoxy functionality, having a number average molecular weight (M_(n)) ofbetween about 1500 and about 10,000 and a glass transition temperature(Tg) of between about -25° and about 70° C., the copolymer consisting of(i) between about 5 and about 25 weight percent of monoethylenicallyunsaturated monomers bearing glycidyl functionality and between about 5and about 25 weight percent of monoethylenically unsaturated monomersbearing hydroxy functionality, with the total of the monoethylenicallyunsaturated monomers bearing either said glycidyl functionality or saidhydroxy functionality being not greater than about 30 weight percent ofthe monomers in the bifunctional copolymer, and (ii) between about 90and about 70 weight percent of other monoethylenically unsaturatedmonomers;

(B) a reactive catalyst comprising at least one oligomeric hydroxyfunctional organophosphate ester having the formula: ##STR1## whereinn=1 to 2 and R is selected from the group consisting of mono- ordihydroxy radicals containing one or more ester linkages and having amolecular weight of between about 120 and about 1500;

(C) an amine aldehyde crosslinking agent; and

(D) up to about 45 weight percent based on the total weight of (A), (B),(C) and (D) of a hydroxy functional additive having a number averagemolecular weight (M_(n)) of between about 150 and about 6,000.

The organophosphate ester is included in the composition in an amountsufficient to provide between about 0.8 and about 1.5 equivalents,preferably between about 0.9 and about 1.2 equivalents, of acidfunctionality for each equivalent of pendent epoxy functionality on thebifunctional copolymer. The amino crosslinking agent is included in thecomposition in an amount sufficient to provide at least about 0.4equivalents, preferably between about 0.6 and about 2.1 equivalents, ofnitrogen crosslinking functionality for each equivalent of hydroxyfunctionality included in the composition either as (i) an organichydroxyl group on said oligomeric hydroxy functional organophosphateester, (ii) a hydroxyl group on said bifunctional copolymer, (iii) ahydroxyl group on said hydroxy functional resin, or (iv) as a result ofesterification of the pendent epoxy functionality of said bifunctionalcopolymer during cure of the composition. In addition, the high solidscoating composition of the invention may include additives such ascatalysts, antioxidants, U.V. absorbers, flow control or wetting agents,antistatic agents, pigments, plasticizers, solvents, etc.

PRIOR ART

U.S. Pat. Nos. 3,960,979 and 4,018,848 to Khanna teach high solidscoating compositions adapted for use as a can coating material. Thecompositions consist essentially of (i) aromatic epoxide compositionshaving two or more epoxy groups on an epoxy resin which has a molecularweight not exceeding 2500; (ii) an amino crosslinking agent; (iii) aninorganic or organic monomeric or polymeric acid which acts as areactive catalyst; and (iv) a flexiblizing polyol.

The compositions of Khanna have the advantage of quick reaction and lowapplication viscosity, but lack durability, and, therefore, do notweather well. This is, in part, because of the presence of etherlinkages in the aromatic epoxides. As such, the compositions of Khannaare not desirable for use as automotive topcoats. The Khanna patentsdescribe the compositions as a low cure system. However, whenconsidering the specific teachings of the patents one finds that thecomposition includes an excess of epoxide resin, apparently with thepurpose of "killing off" excess catalyst after completion of the curingreaction. Excess epoxy resin in the composition remains uncured at thelow temperature bake range of the baking temperatures disclosed, notgiving a complete cure and desirable hardness, durability or solventresistance. If heated to higher temperatures, as called for in theexamples, the excess epoxy does react with excess hydroxy functionalityto give still further ether linkages. These ether linkages so obtainedhave a further deleterious effect on durability and make the materialsparticularly unsuitable for use as an automotive topcoat. Also, thenecessary high bake temperatures to achieve the utilization of thisexcess epoxy makes the composition undesirable from an energy point ofview because of the high baking temperatures required. Still further,because the epoxy/catalyst reaction occurs in early stages of the cure,thus "killing off" the catalyst, the melamine-hydroxy curing reactionmust proceed substantially without benefit of catalysis. The curingreaction thus proceeds slowly and requires the higher temperatures ofthe Khanna examples.

DETAILED DESCRIPTION OF THE INVENTION

The high solids coating compositions of this invention overcomedisadvantages of prior art high solids compositions, including those ofKhanna, to provide a system which is particularly suitable for thoseapplications requiring high gloss, hardness, durability, and highsolvent and water resistance as well as a fast cure rate at lowtemperatures, e.g., between about 75° C. and about 150° C., preferablybetween about 110° C. and about 130° C. The desirable characteristics ofthe coating compositions of this invention result from the carefullycontrolled admixture of the particular components, including anoligomeric hydroxy functional organophosphate ester, to achievesubstantially complete utilization of reactant functionality and aresultant highly crosslinked coating in a fast and efficient manner.

Each of the components of the high solids coating compositions, theamounts of each of the components required to achieve the desiredresults of the invention and a method for applying the composition aredescribed hereinafter in greater detail.

Bifunctional Copolymer

A principal material in the high solids coating compositions of thisinvention is a bifunctional copolymer bearing both hydroxy functionalityand pendent epoxy functionality and which may be prepared byconventional free radical induced polymerization of suitable unsaturatedmonomers. The term "copolymer" as used herein means a copolymer of twoor more different monomers.

The copolymers used in the high solids coating compositions of thisinvention have a number average molecular weight (M_(n)) of betweenabout 1500 and about 10,000, preferably between about 2,000 and about6,000, and a glass transition temperature (Tg) of between about -25° C.and about 70° C., preferably between about -10° C. and about 50° C. Themonomers used to prepare the copolymer include between about 5 and about25 weight percent of one or more monoethylenically unsaturated monomersbearing glycidyl functionality and between about 5 and about 25 weightpercent of one or more monoethylenically unsaturated monomers bearinghydroxy functionality, with the total of the monoethylenicallyunsaturated monomers bearing either epoxy or hydroxy functionality beingnot greater than about 30 weight percent of the monomers in thecopolymer. The monoethylenically unsaturated monomers bearing glycidylfunctionality may be either glycidyl ethers or glycidyl esters.Preferably, however, the epoxy functional monomers are glycidyl estersof monoethylenically unsaturated carboxylic acids. Examples are glycidylacrylates and glycidyl methacrylates. These monomers provide thebifunctional copolymer with the pendent epoxy functionality.

The monoethylenically unsaturated hydroxy functional monomers useful inpreparation of the copolymer and providing the hydroxy functionality tothe bifunctional copolymer may be selected from a long list of hydroxyfunctional monomers. Preferably, however, the hydroxy functionalmonomers are acrylates and may be selected from the group consisting of,but not limited to, the following esters of acrylic or methacrylic acidsand aliphatic alcohols:

2-hydroxyethyl acrylate; 3-chloro-2-hydroxypropyl acrylate;

2-hydroxy-1-methylethyl acrylate; 2-hydroxypropyl acrylate;

3-hydroxypropyl acrylate; 2,3 dihydroxypropyl acrylate;

2-hydroxy-butyl acrylate; 4-hydroxybutyl acrylate;

diethylene-glycol acrylate; 5-hydroxypentyl acrylate;

6-hydroxyhexyl acrylate; triethyleneglycol acrylate;

7-hydroxyheptyl acrylate; 2-hydroxymethyl methacrylate;

3-chloro-2-hydroxypropyl methacrylate; 2-hydroxy-1-methylethylmethacrylate; 2-hydroxypropyl methacrylate;

3-hydroxypropyl methacrylate; 2,3 dihydroxypropyl methacrylate;2-hydroxybutyl methacrylate; 4-hydroxybutyl methacrylate;3,4-dihydroxybutyl methacrylate; 5-hydroxypentyl methacrylate;6-hydroxyhexyl methacrylate; 1,3-dimethyl-3-hydroxybutyl methacrylate;5,6 dihydroxyhexyl methacrylate; and 7-hydroxyheptyl methacrylate.

Although one of ordinary skill in the art will recognize that manydifferent hydroxyl bearing monomers, including those listed, above couldbe employed, the preferred hydroxy functional monomers for use in thebifunctional copolymer of the invention are C₅ -C₇ hydroxy alkylacrylates and/or C₅ -C₇ hydroxy alkyl methacrylates; i.e., esters of C₂-C₃ dihydric alcohols and acrylic or methacrylate acids.

The remainder of the monomers forming the bifunctional copolymer, i.e.,between about 90 and about 70 weight percent of the monomers of thecopolymer, are other monoethylenically unsaturated monomers. Thesemonoethylenically unsaturated monomers are preferably alpha betaolefinically unsaturated monomers, i.e., monomers bearing olefinicunsaturation between the two carbon atoms in the alpha and betapositions with respect to the terminus of an aliphatic carbon-to-carbonchain.

Among the alpha-beta olefinically unsaturated monomers which may beemployed are acrylates (meaning esters of either acrylic or methacrylicacids) as well as mixtures of acrylates and vinyl hydrocarbons.Preferably, in excess of 50 weight percent of the total of the copolymermonomers are esters of C₁ -C₁₂ monohydric alcohols and acrylic ormethacrylic acids, e.g., methylmethacrylate, ethylacrylate,butylacrylate, butylmethacrylate, hexylacrylate, 2-ethylhexylacrylate,laurylmethacrylate, etc. Among the monovinyl hydrocarbons suitable foruse in forming the copolymers are those containing 8 to 12 carbon atomsand including styrene, alpha methylstyrene, vinyl toluene,t-butylstyrene and chlorostyrene. When such monovinyl hydrocarbons areemployed, they should constitute less than 50 weight percent of thecopolymer. Other monomers such as vinyl chloride, acrylonitrile,methacrylonitrile, and vinyl acetate may be included in the copolymer asmodifying monomers. However, when employed, these modifying monomersshould constitute only between about 0 and about 30 weight percent ofthe monomers in the copolymer.

In preparing the bifunctional copolymer, the epoxy functional monomers,the hydroxy functional monomers and the remaining monoethylenicallyunsaturated monomers are mixed and reacted by conventional free radicalinitiated polymerization in such proportions as to obtain the copolymerdesired. A large number of free radical initiators are known to the artand are suitable for the purpose. These include: benzooyl peroxide;lauryl peroxide; t-butylhydroxy peroxide; acetylcyclohexylsulfonylperoxide; diisobutyryl peroxide; di-(2-ethylhexyl) peroxydicarbonate;diisopropylperoxydicarbonate; t-butylperoxypivalate; decanoyl peroxide;azobis (2-methylpropionitrile), etc. The polymerization is preferablycarried out in solution using a solvent in which the bifunctionalcopolymer is soluble. Included among the suitable solvents are toluene,xylene, dioxane, butanone, etc. If the bifunctional copolymer isprepared in solution, the solid copolymer can be precipitated by pouringthe solution at a slow rate into a nonsolvent for the copolymer, such ashexane, octane, or water, under suitable agitation conditions.

The bifunctional copolymer useful in the compositions of this inventioncan also be prepared by emulsion polymerization, suspensionpolymerization, bulk polymerization, or combinations thereof, or stillother suitable methods. In these methods of preparing copolymers, chaintransfer agents may be required to control molecular weight of thecopolymer to a desired range. When chain transfer agents are used, caremust be taken so they do not decrease the shelf stability of thecomposition by causing premature chemical reactions.

Organophosphate Ester

A second essential component of the high solids coatings of thisinvention is a reactive catalyst which comprises a novel oligomerichydroxy functional organophosphate ester which is present in thecomposition as a mono- or diester or as a mixture of such mono- anddiesters. The oligomeric hydroxy functional organophosphate estersuseful in the compositions of the invention are those having theformula: ##STR2## wherein n=1 to 2 and R is selected from the groupconsisting of mono- or dihydroxy radicals containing one or more esterlinkages and having a molecular weight of between about 120 and about1500.

A preferred method for preparing the oligomeric hydroxy functionalorganophosphate esters useful in compositions of the invention is by anesterification reaction between an excess of a di- or trihydroxy alkyl,cycloalkyl or aryl oligoester and phosphorus pentoxide. When atrihydroxy oligoester is used as a reactant, preferably at least one ofthe hydroxyl groups should be secondary. The reaction between the di- ortrihydroxy oligoester and the phosphorus pentoxide is generally carriedout by adding phosphorus pentoxide portionwise to an excess of the di-or trihydroxy oligoester in a liquid state or in solution in a suitablesolvent. Suitable solvents include, but are not limited to, butylacetate, methyl ethyl ketone, toluene, xylene, etc.

The hydroxy functional oligoesters useful in preparing the oligomerichydroxy functional organophosphate esters used in the compositions ofthe invention have a molecular weight of between about 120 and about1500. Such oligoesters may be prepared in accordance with numerousprocedures recognized in the art. For example, the hydroxy functionaloligoesters may be selected from the group consisting of: (i) dihydroxyoligoesters prepared by reacting a dicarboxylic acid with a monoepoxide,(ii) trihydroxy oligoesters prepared by reacting a monohydroxydicarboxylic acid with a monoepoxide; (iii) dihydroxy oligoestersprepared by reacting a monocarboxylic acid with a diepoxide; (iv)trihydroxy oligoesters prepared by reacting a monocarboxylic acid with amonohydroxy diepoxide; (v) dihydroxy oligoesters prepared by reacting amonohydroxy monocarboxylic acid with a monoepoxide; (vi) trihydroxyoligoesters prepared by reacting a monohydroxycarboxylic acid with amonohydroxy monoepoxide; (viii) trihydroxy oligoesters prepared byreacting a monocarboxylic acid with a dihydroxy monoepoxide; (ix)dihydroxy oligoesters prepared by reacting a monocarboxylic acid with amonohydroxy monoepoxide; and (x) di- or trihydroxy oligoesters preparedby reacting polycaprolactones with diols or triols.

Dihydroxyoligoesters prepared by reacting a dicarboxylic acid with amonoepoxide and designated by (i) above are well known in the art. Themost common of this group is a low molecular weight adduct of analiphatic, cycloaliphatic or aryl dicarboxylic acid and a monoepoxide.Most commonly used monoepoxides are alkylene oxides such as ethyleneoxide or propylene oxide. Among the numerous dicarboxylic acids whichmay be used are malonic acid, succinic acid, glutaric acid, 1,9nonanedioic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid,etc. Preferred dicarboxylic acids are C₆ -C₁₂ aliphatic acids as well asmixtures of these acids or mixtures of the aliphatic dicarboxylic acidswith cycloaliphatic or aromatic dicarboxylic acids. The above describedadducts, which arte prepared by reacting the acid and epoxide in thepresence of a catalyst, have a narrow molecular weight distribution whencompared to similar compositions made by normal polyester manufacturingtechniques. While the specific reactants enumerated above will result incompounds containing two (2) ester groups, it will be appreciated thatadditional ester linkages may be present in the compound as a result ofbeing included as a part of a radical born by either the monoepoxide orthe dicarboxylic acid. For example, an oligoester bearing more than twoester linkages may be prepared by reacting dicarboxylic acid withglycidyl carboxylate. This reaction results in a dihydroxy oligoesterbearing four (4) ester linkages. Of course, various other combinationsof dibasic acids and monoepoxides will be apparent to the skilledartisan.

In preparing the trihydroxy oligoesters designated as (ii) above,numerous monohydroxy dicarboxylic acids may be employed in lieu of thedicarboxylic acids previously described. Representative of thesemonohydroxy aliphatic, cycloaliphatic or aromatic dicarboxylic acids aremalic acid, hydroxyglutaric acid, 2-hydroxy-1,4-cyclohexanedicarboxylicacid and 2-methylol terephthalic acid. As with oligoesters designated by(i) above, the preferred monohydroxydicarboxylic acids are C₆ -C₁₂aliphatic acids, mixtures of those acids or mixtures of those acids withcycloaliphatic or aromatic dicarboxylic acids.

In preparing dihydroxy oligoesters designated as (iii) above, amonocarboxylic acid is reacted with a diepoxide. Representative of thenumerous aliphatic, cycloaliphatic or aromatic monocarboxylic acidswhich may be used are pentanoic acid, hexanoic acid, heptanoic acid,cyclohexane carboxylic acid and benzoic acid. Preferred monocarboxylicacids are acetic acid, propionic acid and butyric acid. Among thenumerous suitable diepoxides which will be apparent to those skilled inthe art are: cycloaliphatic diepoxides and glycidyl ethers of aliphaticand aromatic dihydroxy compounds. As was the case above, polyesterlinkages other than those resulting from the esterification reactionbetween the acid and epoxy groups may be included by using acids ordiepoxides containing a radical bearing one or more ester linkages. Forexample, acetic acid could be reacted withbis-(3,4-epoxy-6-methylcyclohexyl methyladipate to yield an oligoesterwith four (4) ester linkages.

Trihydroxy oligoesters designated (iv) may be prepared by reactingmonocarboxylic acids such as described in (iii) with monohydroxydiepoxides. Typical monohydroxy diepoxides are: hydroxyglycidyl ethersof bisphenol A and aliphatic hydroxyglycidyl resins. As above, radicalsbearing additional ester linkages may be included in the acid ordiepoxide.

Dihydroxy oligoesters designated as (v) above may be prepared byreacting a monohydroxy monocarboxylic acid with a monoepoxide.Representative of the numerous aliphatic, cycloaliphatic or aromaticmonohydroxy monocarboxylic acids are 3-hydroxybutyric acid,4-hydroxycyclohexylcarboxylic acid and 4-methylol benzoic acid.

Suitable monoepoxides are enumerated above in the discussion ofoligoesters (i) and (ii). As in all cases, radicals bearing additionalester linkages may be included.

The trihydroxy oligoester of (vi) is a variation of (v) with thereactants being a monoepoxide as above and a dihydroxymonocarboxylicacid such as 3,4-dihydroxybutyric acid and glyciric acid.

The trihydroxy oligoester of (vii) is prepared by reacting a monohydroxymonocarboxylic acid such as in (v) above with a monohydroxy monoepoxidesuch as, for example, glycidol and 1,4-butanediolmonoglycidyl ether. Asin other cases, additional ester linkages may also be included in theoligoester.

The trihydroxy oligoester designated (viii) may be prepared by reactinga monocarboxylic acid as above with a dihydroxy monoepoxide such asacetic acid with 2,3 epoxy-1,4-butane diol. Additional ester linkagesmay be included, if desired.

The dihydroxy oligoester (ix) is prepared by reacting a monocarboxylicacid with a monohydroxy monoepoxide. Both reactants are discussed aboveand, as in other cases, additional ester linkages may be added usingester bearing radicals.

Hydroxy functional oligoesters of the type designated by (x) above areknown in the art. Polycaprolactones, such as caprolactone, reacted withdiols yield dihydroxy oligoesters while reaction with triols yieldstrihydroxy oligoesters.

A preferred temperature for carrying out the reaction between thehydroxy functional oligoester and the phosphorus pentoxide is betweenabout 50° C. and about 55° C. Due to the multiple hydroxy functionalityof the dior- or trihydroxy oligoester, minor amounts of polymeric acidphosphate as well as certain cyclophosphates are also generated duringthe synthesis. These polymeric and cyclic materials also serve as areactive catalyst and, therefore, need not be separated from thehydroxyphosphate esters described above. In fact, it has been foundadvantageous in preferred embodiments of the invention to employ allreaction products, i.e., the oligomeric hydroxy functionalorganophosphate esters and the minor amount of polymeric acid phosphatecyclophosphates, as well as excess di- or trihydroxy oligoester in thecoating compositions. The excess di- or trihydroxy oligoester serves inthose compositions as the optional hydroxy functional additive. Reactivecatalysts prepared by the above preferred method will generally includeabout a 1 to 1 ratio of the mono- and diester organophosphate.

The oligomeric hydroxy functional organophosphate ester component of thehigh solids coating composition of the invention is a reactive catalystwhich allows the composition to cure rapidly at a low temperature. Theacid functionality of the mono- or diester or mixture of such estersreacts with the pendent epoxy functionality of the bifunctionalcopolymer to form an ester and a hydroxyl group. This hydroxyl group, aswell as the organic hydroxyl groups on the oligomeric hydroxy functionalorganophosphate ester, the additional hydroxy functionality on thebifunctional copolymer and any optional hydroxy groups included in thecomposition in the form of hydroxy functional additive, including excessdi- or trihydroxy oligoester present from the synthesis of theoligomeric hydroxy functional organophosphate ester, crosslinks with theamino resin crosslinking agent. It is critical to achieving the mostpreferred results of the high solids coating compositions of thisinvention, i.e., in making them suitable for use as automotive topcoats,that the amount of the oligomeric hydroxy functional organophosphateester be sufficient to convert substantially all of the epoxyfunctionality on the bifunctional copolymer to the desired hydroxyfunctionality by esterification reaction. Therefore, the organophosphateester is included in the composition in an amount sufficient to providebetween about 0.8 and about 1.5 equivalents, preferably between about0.9 and about 1.2 equivalents, of acid functionality for each equivalentof pendent epoxy functionality on the bifunctional copolymer. As will benoted from the equivalent amounts of epoxy and organophosphate acidester functionality stated above, the acid functionality need not be instoichiometric amounts to the epoxy functionality. This is because ofthe fact that during curing of the high solids coating composition,residual water present in the composition hydrolyzes some of theesterified product back to acid and this esterified product then, inturn, reacts with additional epoxy functionality.

Amino Crosslinking Agent

A third essential component of the high solids paint compositions ofthis invention is an amino resin crosslinking agent. Amino crosslinkingagents suitable for crosslinking hydroxy functional bearing materialsare well known in the art. Typically, these crosslinking materials areproducts of reactions of melamine, or urea with formaldehyde and variousalcohols containing up to and including 4 carbon atoms. Preferably, theamino crosslinking agents useful in this invention are amine-aldehyderesins such as condensation products of formaldehyde with melamine,substituted melamine, urea, benzoguanamine or substitutedbenzoguanamine. Preferred members of this class are methylatedmelamine-formaldehyde resins such as hexamethoxymethylmelamine. Theseliquid crosslinking agents have substantially 100 percent nonvolatilecontent as measured by the foil method at 45° C. for 45 minutes. For thepurposes of the invention it should be recognized that it is importantnot to introduce extraneous diluents that would lower the final solidscontent of the coating.

Particularly preferred crosslinking agents are those sold by AmericanCyanamid under the trademark "Cymel". In particular, Cymel 301, Cymel303 and Cymel 1156, which are alkylated melamine-formaldehyde resins,are useful in the compositions of the invention by reacting with hydroxyfunctionality included in the composition (i) as an organic hydroxylgroup on the oligomeric hydroxy functional organophosphate ester, (ii)as hydroxy functionality on the bifunctional copolymer, (iii) as hydroxyfunctionality on the optional hydroxy functional additive, or (iv) as aresult of esterification of the pendent epoxy functionality on thebifunctional copolymer.

In order to achieve the outstanding properties which make these coatingcompositions particularly useful as automoive topcoat materials, it isessential that the amount of amino crosslinking agent be sufficient tosubstantially completely crosslink the hydroxy functionality in thecoating composition. Therefore, the amino resin crosslinking agentshould be included in the composition in an amount sufficient to provideat least about 0.4 equivalents, preferably between about 0.6 and about2.1 equivalents, of nitrogen crosslinking functionality for eachequivalent of hydroxy functionality included in the composition.

Optional Hydroxy Functional Additive

Additional hydroxy functionality other than that achieved byesterification of pendent epoxy functionality of the bifunctionalcopolymer or by the oligomeric hydroxy functional organophosphate estermay be achieved by adding a hydroxy functional additive in amounts up toabout 45 weight percent based on the total of the three above discussedcomponents and the hydroxy functional additive itself. Such a materialserves to provide additional hydroxy functionality so as to provide amore intimate crosslinked structure in the final cured product. Thehydroxy functional additives useful in the composition are preferablyselected from various polyols have a number average molecular weight(M_(n)) of between about 150 and about 6,000, preferably between about400 and about 2500. As used herein the term polyol means a compoundhaving two or more hydroxyl groups.

The polyols useful for the invention preferably are selected from thegroup consisting of: (i) hydroxy functional polyesters; (ii) hydroxyfunctional polyethers; (iii) hydroxy functional oligoesters, (iv)monomeric polyols; (v) hydroxy functional copolymers produced by freeradical polymerization of monoethylenically unsaturated monomers, one ormore of which bears hydroxy functionality and which is included in thecopolymer in an amount ranging from about 2.5 to about 30 weight percentof the copolymer; and (vi) mixtures of (i)-(v).

The hydroxy functional polyesters useful in the invention are preferablyfully saturated products prepared from aliphatic dibasic acidscontaining 2-20 carbon atoms, such as succinic acid, glutaric acid,adipic acid, azelaic acid, etc., and short chain glycols of up to andincluding 21 carbon atoms, such as ethylene glycol, 1,2-propyleneglycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol,1,4-butylene glycol, neopentyl glycol, 1,4-cyclohexane dimethylol,1,6-hexamethylene glycol and 2-ethyl-2-methyl-1,3 propane diol. Themolecular weight of these materials ranges from about 150 to about 3000and the hydroxyl number ranges from about 30 to about 230. The hydroxylnumber is defined as the number of milligrams of potassium hydroxideneeded for each gram of sample to neutralize the acetic acid generatedduring the reaction between the polyol and excess acetic anhydride. Thepolyester polyols utilized in the invention are low melting, soft waxysolids which are easily maintained in the molten state.

Among preferred polyesters are products derived from the esterificationof ethylene glycol and 1,4 butane diol with adipic acid, ethylene glycoland 1,2 propylene glycol with adipic acid, azelaic acid and sebacic acidcopolyester diols, and mixtures thereof.

Among useful polyether diols are polytetramethylene ether glycol,polyethylene glycol, polypropylene glycol and the like.

The hydroxy functional oligoesters useful as hydroxy functionaladditives in the compositions of the invention are oligoesterspreferably having a molecular weight of between about 150 and about3000. Included in this class of materials are the di- or trihydroxyoligoesters described above for use in preparing the oligomeric hydroxyphosphate ester catalysts of the invention. Similar oligoester withmolecular weights greater than the 1500 limit of those oligoesters up tothe 3000 limit specified above as well as similarly prepared oligoestersbearing more than three hydroxyl groups may be employed.

Among the numerous monomeric polyols which may be employed as thehydroxy functional additive are the various short chain glycols of up toand including 21 carbon atoms which are useful in preparing the hydroxyfunctional polyesters discussed above. Other conventional polyhydricalcohols such as glycerols and sugar alcohols are also among thenumerous monomeric polyols which will be apparent to those skilled inthe art. Triols which may be used in the synthesis of the hydroxyfunctional organophosphate ester may be employed as all or part of themonomeric polyol in the composition of the invention.

The hydroxyl bearing copolymer useful as the hydroxy functional additivemay be formed from monoethylenically unsaturated monomers, with betweenabout 2.5 and 30 weight percent bearing hydroxy functionality.

The suitable hydroxy functional monomers for preparation of the hydroxyfunctional resins useful in the invention are the same as those usefulin preparation of the bifunctional copolymer discussed above.

The remainder of the monomers forming the hydroxy functional copolymer,i.e., between about 90 and about 70 weight percent, are othermonoethylenically unsaturated monomers. These monoethylenicallyunsaturated monomers, as was the case with respect to the bifunctionalcopolymer discussed above, are preferably alpha-beta olefinicallyunsaturated monomers. As was also the case with respect to thebifunctional copolymer, the preferred alpha-beta olefinicallyunsaturated monomers are acrylates and preferably are employed in excessof 50 weight percent of the total copolymer. Preferred acrylate monomersare esters of C₁ -C₁₂ monohydric alcohols and acrylic or methacrylicacids. Monovinyl hydrocarbons and other modifying monomers may also beemployed in the same proportion as they are employed in the bifunctionalcopolymer discussed above.

Other Materials

In addition to the above discussed components, other materials may beincluded in the high solids coating compositions of the invention. Theseinclude materials such as catalysts, antioxidants, U.V. absorbers,solvents, surface modifiers and wetting agents as well as pigments. Thesolvents used in the coating compositions of the invention are thosewhich are commonly used. Typical solvents useful in the coatingcompositions facilitate spray application at high solids content andinclude toluene, xylene, methyethyl ketone, acetone, 2-ethoxy-1-ethanol,2-butoxy-1-ethanol, diacetone alcohol, tetrahydrofuran, ethylacetate,dimethylsuccinate, dimethylglutarate, dimethyladipate or mixturesthereof. The solvent in which the bifunctional copolymer of the coatingcomposition is prepared, may be employed as the solvent for the coatingcomposition, thus eliminating the need for drying the bifunctionalcopolymer after preparation if such is desired. As mentioned above, thenonvolatile solids content of the high solids coating composition is atleast 60 percent and preferably 70 percent or more, thus limiting theamount of solvent included in the composition.

Surface modifiers or wetting agents are common additives for liquidpaint compositions. The exact mode of operation of these surfacemodifiers is not known, but it is thought that their presencecontributes to better adhesion of the coating composition to the surfacebeing coated and helps formation of thin coatings on surfaces,particularly metal surfaces. These surface modifiers are exemplified byacrylic polymers containing 0.1-10 percent by weight of a copolymerizedmonoethylenically unsaturated carboxylic acids such as methacrylic acid,acrylic acid or itaconic acid, cellulose acetate butyrate, silicon oilsor mixtures thereof. Of course, the choice of surface modifier orwetting agent is dependent upon the type of surface to be coated andselection of the same is clearly within the skill of the artisan.

The high solids coating composition of the invention also may includepigments. As noted above, the high solids composition of this inventionare particularly useful when the coating composition includes metallicflake as a pigment. The rapid set and curing of the compositioneliminates problems associated with redistribution of the metallic flakein the composition. The amount of pigment in the high solids coatingcomposition may vary, but preferably is between about 3 and about 45weight percent based on the total weight of the paint composition. Ifthe pigment is metallic flake, the amount ranges from about 1 to about 7weight percent.

Application Techniques

The high solids coating composition can be applied by conventionalmethods known to those in the art. These methods include roller coating,spray coating, dipping or brushing and, of course, the particularapplication technique chosen will depend on the particular substrate tobe coated and the environment in which the coating operation is to takeplace.

A particularly preferred technique for applying the high solids coatingcompositions, particularly when applying the same to automobiles astopcoats, is spray coating through the nozzle of a spray gun.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that the specific examplesare presented by way of illustration and not by way of limitation.Unless otherwise specified, all references to "parts" is intended tomean parts by weight.

EXAMPLE 1

(a) 941 grams of azelaic acid are heated to melt in a three-necked flaskequipped with a stirring rod, dropping funnel and a condenser. Sixteengrams of Cordova Accelerator (AMC-2) are added to the above melt and 725grams of propylene oxide are added dropwise with continuous stirring;ice-cold water is continuously circulated through the condenser. Afterthe addition is complete, the reaction mixture is heated for half anhour and then a slight vacuum is applied to remove any excess propyleneoxide.

Five hundred (500) grams of the above ester, bis(hydroxypropyl) azelate,are placed under nitrogen in a three-necked flask and powderedphosphorus pentoxide is added with continuous stirring. An exothermicreaction occurs; the addition of P₂ O₅ is regulated to maintain thetemperature at 50°-55° C. The addition of P₂ O₅ is continued until theacid equivalent weight of the reaction mixture has reached 430. Thereaction mixture is allowed to stay overnight and then titrated with KOHsolution to obtain an acid equivalent weight of 398.

(b) In a three-necked, round bottom, two liter flask, equipped with astirrer, a condenser and a dropping funnel, 750 ml of toluene is broughtto reflux under nitrogen. The following mixture of monomers, containing15 grams of 2,2'-azobis-(2-methyl propionitrile) dissolved in 50 mlacetone, is added dropwise to the refluxing toluene.

    ______________________________________                                                      Weight Gram                                                                             Weight Percent                                        ______________________________________                                        Butyl methacrylate                                                                            150         50                                                Glycidyl methacrylate                                                                         45          15                                                Hydroxypropyl methacrylate                                                                    30          10                                                Methyl methacrylate                                                                           60          20                                                Styrene         15           5                                                ______________________________________                                    

The addition of the initiator and monomer solution is completed in threehours. The reaction mixture is refluxed for half an hour more and 10 mlof an acetone solution of 2 grams of the above initiator is addeddropwise and the reaction mixture refluxed for half an hour. Part of thesolvent is distilled out to bring the solids content to 66% by weight.

Twenty (20) parts of (b) are mixed with 9 parts of Cymel 301 and themixture dissolved in ten (10) parts of butyl acetate. 6.6 parts ofhydroxy phosphate (a) is added to the above solution and the resultingformulation drawn on a steel test panel. The panel is baked at 125° C.for 20 minutes to obtain a coating with excellent hardness, adhesion andsolvent (xylene and methyl ethyl ketone) resistance.

EXAMPLE 2

Twenty-five (25) parts of the copolymer solution described in Example1(b), sixteen (16) parts of Cymel 301 and twelve (12) parts of polyesterDesmophen KL5-2330 (Mobay Chemical Company) are dissolved in 12 parts ofbutyl acetate. Hydroxy phosphate reaction from Example 1(a), 8.5 parts,is added to the above solution and the resulting formulation sprayapplied to primed test panels. The panels are baked at 130° C. for 20minutes to obtain a coating with excellent hardness, adhesion andsolvent (xylene and methyl ethyl ketone) resistance.

EXAMPLE 3

(a) 524 grams of bis-(hydroxypropyl) adipate are prepared from adipicacid and propylene oxide by following the method described forbis-(hydroxypropyl) azelate in Example 1(a). By following the proceduredescribed in Example 1(a), oligomeric hydroxyphosphate with an acidequivalent weight of 315 is prepared from this dihydroxy ester.

(b) A copolymer is prepared by following the procedure described inExample 1(a) in methyl amyl ketone at 125° C. and by using the followingmonomers:

    ______________________________________                                                            Weight Percent                                            ______________________________________                                        Butyl methacrylate    50                                                      Ethylhexyl acrylate   10                                                      Glycidyl methacrylate 15                                                      Hydroxypropyl methacrylate                                                                          10                                                      Methyl methacrylate   10                                                      Styrene                5                                                      ______________________________________                                    

Tert-butyl peroctoate (5.25% of monomers) is used as an initiator andthe determined solids content is 56.6% by weight. The calculated Tg ofthe copolymer is 25° C. and the molecular weight from Gel PermeationChromatography is found to be Mn=4220 and M_(w) /M_(n) =1.90.

A millbase is prepared by dispensing titanium dioxide in polymersolution a high speed Cowl's blade. The composition of the millbase is:15% polymer (100% nonvolatile), 65% titanium dioxide and 20% methyl amylketone. Seventy-two (72) parts of this millbase, 31 parts of thepolymer, 5 parts of bis-(hydroxypropyl) azelate, 29 parts of Cymel 301and 21 parts of methyl amyl ketone are taken up in a plastic bottle. 9.5parts of hydroxy phosphate reaction product (a) (equivalent weight 315),are added to the above mixture and the resulting formulation sprayapplied to both primed and unprimed steel panels. The panels are bakedat 130° C. for 20 minutes to obtain hard, glossy coatings with excellentadhesion. The coating has excellent solvent and humidity resistance.

EXAMPLE 4

By following the procedure described in Example 3(b), a copolymer isprepared from the following monomers:

    ______________________________________                                                           Weight Percent                                             ______________________________________                                        Butyl methacrylate   60                                                       Glycidyl methacrylate                                                                              20                                                       Hydroxyethyl acrylate                                                                              10                                                       Styrene              10                                                       ______________________________________                                    

The calculated Tg of the polymer is 25° C. and solids content is foundto be 54.9% by weight. The molecular weight by Gel PermeationChromotography is found to be Mn=1809 and Mw/Mn=2.44. In the mannerdescribed in Example 3, a millbase is prepared from the followingmaterials:

    ______________________________________                                        Copolymer       21%      (100% nonvolatile)                                   Titanium dioxide                                                                              61%                                                           Methyl amyl ketone                                                                            18%                                                           ______________________________________                                    

Sixty-five (65) parts of this millbase, 27 parts of the above polymer, 5parts bis-(hydroxyl propyl) azelate, 25 parts Cymel 301 and 20 parts ofmethyl amyl ketone are taken up in a plastic bottle. Hydroxy phosphatereaction product from Example 1(a) (equivalent weight 398), 17.9 parts,is added to the above mixture and the resulting formulation sprayapplied to both primed and unprimed panels. The panels are baked at 130°C. for 20 minutes to obtain hard coatings with excellent adhesion andsolvent resistance.

EXAMPLE 5

By following the procedure described in Example 3(b), a copolymer isprepared from the following monomers.

    ______________________________________                                                            Weight Percent                                            ______________________________________                                        Butyl methacrylate    49                                                      Glycidyl methacrylate 20                                                      Hydroxypropyl methacrylate                                                                          10                                                      Methyl methacrylate   16                                                      Styrene                5                                                      ______________________________________                                    

The calculated Tg of the copolymer is 43° C. and solids content is foundto be 52%. The molecular weight, by Gel Permeation Chromatography, isfound to be, Mn=2904 and M Mw/Mn=2.31.

One hundred (100) parts of the above polymer solution are mixed with 5.5parts of aluminum flakes (65% in naphtha), 31 parts of Cymel 301 and 10parts of butyl acetate. Thirty (30) parts of the hydroxyphosphatereaction product from Example 1(a) are added to the above mixture andthe resulting formulation is applied by spraying in three coats toprimed panels. The panels are baked at 120° C. to obtain a silvermetallic coating with excellent hardness, adhesion and solvent (xyleneand methyl ethyl ketone) resistance.

EXAMPLE 6

By following the procedure described in Example 1(b) a copolymer isprepared in refluxing methyl amyl ketone from the following monomers:

    ______________________________________                                                           Weight Percent                                             ______________________________________                                        Glycidyl methacrylate                                                                              20                                                       Hydroxyethyl acrylate                                                                              10                                                       Butyl methacrylate   60                                                       Styrene              10                                                       ______________________________________                                    

Two percent tert-butyl peroctoate is used as an initiator; the solidscontent is found to be 53.6%. From Gel Permeation Chromotography themolecular weight of the polymer is found to be: Mn=2746 and Mw/Mn=2.33.

As described in Example 3, a millbase is prepared with the followingingredients:

    ______________________________________                                                       Weight Percent                                                 ______________________________________                                        Titanium dioxide 56                                                           The above Polymer                                                                              26      (100% nonvolatile)                                   Methyl amyl ketone                                                                             18                                                           ______________________________________                                    

Seventy-one (71) parts of this millbase, 15 parts polymer, 7 partsbis(hydroxypropyl) azelate, 27 parts Cymel 301, 25 parts methyl amylketone and 16.4 parts hydroxy phosphate reaction product (equivalentweight 398) from Example 1(a) are mixed in a plastic container. Thisformulation is spray applied to primed test panels. The panels are bakedat 130° C. for 20 minutes to obtain glossy, hard coatings with excellentsolvent (xylene and methyl amyl ketone) resistance. The coatings do notshow any loss of gloss, adhesion or solvent resistance upon exposure ina Cleveland Humidity Chamber for 14 days.

EXAMPLE 7

(a) By following the procedure described in Example 1 (a), 586 grams ofa mixture of bis(hydroxypropyl) azelate and bis-(hydroxypropyl)terephthalate are prepared from 188 grams of azelaic acid and 166 gramsof terephthalic acid. Hydroxyphosphate reaction product with an acidequivalent weight of 337 is prepared from the above ester mixture asdescribed in Example 1(a).

(b) By following the procedure described in Example 1 (b), a copolymeris prepared in refluxing toluene from the following monomers:

    ______________________________________                                                            Weight Percent                                            ______________________________________                                        Butyl methacrylate    50                                                      Ethylhexyl acrylate   20                                                      Glycidyl methacrylate 15                                                      Hydroxypropyl methacrylate                                                                          10                                                      Styrene                5                                                      ______________________________________                                    

One thousand grams of the total monomers and 700 ml toluene and 50 gramstert-butyl peroctoate are used. The calculated Tg of this polymer is 6°C. and the solids content is found to be 59% by weight; a Gel PermeationChromatogram shows its molecular weight to be: Mn=4337 and Mw/Mn=2.14.Viscosity of this polymer solution is 1.33 Stokes.

Fifty parts of the copolymer prepared in (b), 21 parts of Cymel 301, and10.55 parts of hydroxy phosphate prepared in (a) are dissolved in 12parts of n-butyl acetate. This formulation is spray applied in threecoats to primed steel panels which are baked at 130° C. for 20 minutesto obtain coatings with excellent physical properties.

EXAMPLE 8

Forty (40) parts of polymer solution from Example 1(b) are mixed with 17parts of butoxymethyl melamine (Cymel 1170), 2 parts ofpolypropyleneglycol (Pluracol P710, BASF Wyandotte) and 20 parts ofbutyl acetate. 11.2 parts Hydroxy-phosphate from Example 7(a) is addedto the above solution and the resulting formulation applied by sprayingto primed steel test panels. The panels are baked at 130° C. for 20minutes to obtain coatings with excellent hardness, adhesion and solvent(xylene and methyl ethyl ketone) resistance.

EXAMPLE 9

By following the procedure described in Example 1(a), 90 grams of3-hydroxypropionic acid were reacted with 73 grams of propylene oxide.The excess propylene oxide was evaporated under reduced pressure and theresulting ester was treated with P₂ O₅, as described in Example 1(a), toobtain hydroxyphosphate reaction product with acid equivalent weight of311. Sixty parts of the polymer solution from Example 7, 27 parts ofCymel 301 and 11.6 parts of the above hydroxyphosphate reaction productare dissolved in 15 parts of n-butyl acetate. This formulation is sprayapplied in three coats to primed steel panels which are baked at 130° C.for 20 minutes to obtain coating with excellent physical properties.

EXAMPLE 10

In the formulation described in Example 2, 17 parts of ethoxymethoxybenzoguanamine (Cymel 1123) are employed as a crosslinking resin insteadof Cymel 301. The resulting formulation is applied by spraying ontoprimed steel test panels. The panels are baked at 130° C. for 20 minutesto obtain coatings with excellent hardness, adhesion and solvent (xyleneand methyl ethyl ketone) resistance.

EXAMPLE 11

In this formulation, components described in Example 3, are employed inexact quantities as described therein except that 39 parts ofbutoxymethyl glycoluril (Cymel 1170) are used as the crosslinking agentinstead of Cymel 301. The formulation is applied by spraying to primedsteel panels and baked at 130° C. for 20 minutes to obtain hard, glossycoatings with excellent adhesion and solvent (xylene and methyl ethylketone) resistance.

EXAMPLE 12

In the formulation described in Example 4, 35 parts of butoxymethylurearesin (Beetle 80, American Cyanamid) are substituted for Cymel 301, andthe resulting formulation spray applied to primed steel panels. Thepanels are baked at 130° C. for 20 minutes to obtain hard, glossycoatings with excellent adhesion and solvent (xylene and methyl ethylketone) resistance.

EXAMPLE 13

Five hundred grams of caprolactone based oligo-diol (mol. wt. 530,PCP-0200, Union Carbide) was treated with P₂ O₅ as described in Example1(a) to obtain a hydroxyphosphate reaction product with acid equivalentweight of 762.

Seventy-five (75) parts of the polymer solution from Example 5 are mixedwith 4 parts of aluminum flakes (65% in naphtha), 33 parts of Cymel 301and 7 parts of butyl acetate. Forty-two (42) parts of the abovehydroxyphosphate are added to this solution and the resultingformulation is spray applied in three coats to primed panels. The panelsare baked at 130° C. for 20 minutes to obtain silver metallic coatingwith excellent hardness, adhesion and solvent (xylene and methyl ethylketone) resistance.

EXAMPLE 14

(a) Two grams of Cordova Accelerator (AMC-2) is mixed with 155 grams ofvinylcyclohexene dioxide and this mixture is added dropwise to 120 gramsof refluxing acetic acid. After the addition is complete, the reactionmixture is stirred at 100° C. for one hour and then is allowed to coolto room temperature. The resulting ester is treated with P₂ O₅, asdescribed in Example 1(a), to obtain a hydroxyphosphate reaction productwith an acid equivalent weight of 336.

(b) A copolymer is prepared from the following monomers by following theprocedure described in Example 1(b).

    ______________________________________                                                            Weight Percent                                            ______________________________________                                        Butyl methacrylate    50                                                      Ethylhexyl acrylate   10                                                      Glycidyl methacrylate 15                                                      Hydroxypropyl methacrylate                                                                          10                                                      Methyl methacrylate   10                                                      Styrene                5                                                      ______________________________________                                    

Toluene is used as solvent to obtain a 60% solution of the polymer;tert-butyl peroctoate (3.7% of monomers) is used as an initiator.Toluene (60%) is distilled off and butyl acetate is added to bring thesolids level to 60% by weight. The calculated Tg of the polymer is 25°C. and the molecular weight by Gel Permeation Chromatography is found tobe Mn=5301, Mw/Mn=2.9.

Three hundred (300) parts of this polymer solution are mixed well with11.2 parts of aluminum flakes (65% in naphtha), 3.2 parts of zincnaphthanate, and 97 parts of hexamethoxymethyl melamine (Cymel 301) areadded to this mixture. 64 parts of hydroxyphosphate reaction productfrom (a) are dissolved in 50 ml of cellusolve acetate; this solution isadded to the above mixture and the resulting formulation applied byspraying to primed steel panels in three coats. The panels are baked at130° C. for 20 minutes to obtain silver metallic coatings with excellentphysical properties.

In view of this disclosure, many modifications of this invention will beapparent to those skilled in the art. It is intended that all suchmodifications which fall within the true scope of this invention beincluded within the terms of the appended claims.

I claim:
 1. A thermosetting coating composition adapted for lowtemperature bake applications which contains greater than about 60% byweight of nonvolatile solids, and which, exclusive of pigments, solventsand other nonreactive components, consists essentially of:(A) abifunctional copolymer bearing hydroxy functionality and pendant epoxyfunctionality, having a number average molecular weight (Mn) of betweenabout 1500 and about 10,000 and a glass transition temperature (Tg) ofbetween about -25° C. and about 70° C., said copolymer consistingessentially of (i) between about 5 and about 25 weight percent ofmonoethylenically unsaturated monomers bearing glycidyl functionalityand between about 5 and about 25 weight percent of monoethylenicallyunsaturated monomer bearing hydroxy functionality, with the total ofsaid glycidyl and hydroxy functional monomers being not greater thanabout 30 weight percent of the monomers in said bifunctional copolymerand (ii) between about 90 and about 70 weight percent of othermonoethylenically unsaturated monomers; (B) a reactive catalystcomprising hydroxy functional organo-phosphate ester having the formula:##STR3## wherein n=1 to 2 and R is selected from the group consisting ofmono or dihydroxy radicals containing one or more ester linkages andhaving a molecular weight of between about 120 and about 1500; (C) anamine-aldehyde crosslinking agent; and (D) up to about 45 weight percentbased on the total weight of (A), (B), (C), and (D) of a hydroxyfunctional additive having a number average molecular weight (Mn) ofbetween about 150 and about 6000, said organophosphate ester beingincluded in said composition in an amount sufficient to provide betweenabout 0.8 and about 1.5 equivalents of acid functionality for eachequivalent of pendent epoxy functionality on said bifunctionalcopolymer, and said amine aldehyde crosslinking agent being included insaid composition in an amount sufficient to provide at least about 0.4equivalents of nitrogen crosslinking functionality for each equivalentof hydroxy functionality included in said composition either as (i) anorganic hydroxyl group on said organophosphate ester, (ii) a hydroxylgroup on said bifunctional copolymer, (iii) a hydroxyl group on saidhydroxy functional additive, or (iv) as a result of esterification ofsaid pendent epoxy functionality of said bifunctional copolymer duringcure of said coating composition.
 2. A composition in accordance withclaim 1, wherein said monoethylenically unsaturated monomers bearingglycidyl functionality in said bifunctional copolymer are selected fromglycidyl esters and glycidyl ethers.
 3. A composition in accordance withclaim 2, wherein said monoethylenically unsaturated monomers bearingglycidyl functionality are selected from glycidyl esters ofmonoethylenically unsaturated carboxylic acids.
 4. A composition inaccordance with claim 1 wherein said monoethylenically unsaturatedmonomers bearing hydroxy functionality in said bifunctional copolymerare selected from the group consisting of hydroxyalkyl acrylates formedby the reaction of C₂ -C₅ dihydric alcohols and acrylic or methacrylicacids.
 5. A composition in accordance with claim 1, wherein said othermonoethylenically unsaturated monomers in said bifunctional copolymerare selected from the group consisting of acrylates and othermonoethylenically unsaturated vinyl monomers.
 6. A composition inaccordance with claim 5 wherein said acrylate monomers comprise at leastabout 50 weight percent of the total monomers in said bifunctionalcopolymer and are selected from its group consisting of esters of C₁-C₁₂ monohydric alcohols and acrylic or methacrylic acids.
 7. Acomposition in accordance with claim 1 wherein said oligomeric hydroxyfunctional organophosphate esters are esters wherein R is a mono- ordihydroxy alkyl, cycloalkyl or aryl radical.
 8. A composition inaccordance with claim 1 wherein said oligomeric hydroxy functionalorganophosphate ester is a monoester.
 9. A composition in accordancewith claim 1 wherein said oligomeric hydroxy functional organophosphateester is a diester.
 10. A composition in accordance with claim 1 whereinsaid oligomeric hydroxy functional organophosphate ester is a mixture ofmono- and diesters.
 11. A composition in accordance with claim 10wherein said oligomeric hydroxy functional organophosphate esters areesters wherein R is a mono- or dihydroxy alkyl, cycloalkyl or arylradical.
 12. A composition in accordance with claim 1 wherein saidoligomeric hydroxy functional organophosphate ester is the reactionproduct of a di- or trihydroxy oligoester and phosphorus pentoxide. 13.A composition in accordance with claim 12 wherein said reactive catalystincluding said oligomeric hydroxy functional organophosphate ester isthe reaction product of an excess of a di- or trihydroxy alkyl,cycloalkyl or aryl oligoester and phosphorus pentoxide.
 14. Acomposition in accordance with claim 12 wherein said reactive catalystincluding said oligomeric hydroxy functional organophosphate ester isthe reaction product of an excess of a trihydroxy alkyl, cycloalkyl oraryl oligoester in which at least one of the hydroxyl groups issecondary, and phosphorus pentoxide.
 15. A composition in accordancewith claim 1 wherein said amine-aldehyde crosslinking agent selectedfrom the group consisting of condensation products of formaldehyde withmelamine, substituted melamine, urea, benzoguanamine and substitutedbenzoguanamine, and mixtures of said condensation products, and isincluded in an amount sufficient to provide between about 0.6 and about2.1 equivalents of nitrogen crosslinking functionality per equivalent ofhydroxy functionality.
 16. A composition in accordance with claim 1,wherein said hydroxy functional additive is selected from the groupconsisting of (i) hydroxy functional polyesters, (ii) hydroxy functionalpolyethers, (iii) hydroxy functional oligoesters, (iv) monomericpolyols; (v) hydroxy functional copolymers formed from monoethylenicallyunsaturated monomers, one or more of which bears hydroxy functionalityand which is included in said copolymer in amounts ranging from about2.5 to about 30 weight percent of said copolymer, and (vi) mixtures of(i)-(v).
 17. A composition in accordance with claim 1 wherein saidorganophosphate ester is included in said composition in an amountsufficient to provide between about 1 and about 1.2 equivalents of acidfunctionality for each equivalent of pendent epoxy functionality on saidbifunctional copolymer.